Reference voltage circuits in microcontroller systems

ABSTRACT

A microcontroller system includes a higher power reference voltage circuit and a lower power reference voltage circuit configured to draw less power than the higher power reference voltage circuit when enabled. The system includes a power state logic controller configured to enable the lower power reference voltage circuit to provide a first regulated voltage during a power saving mode, and, on exiting the power saving mode, enable the higher power reference voltage circuit to provide a second regulated voltage.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.13/603,155 filed Sep. 4, 2012, which claims the benefit and priority ofU.S. Provisional Application Ser. No. 61/676,595, filed Jul. 27, 2012,the entire contents of which are hereby incorporated by reference.

TECHNICAL FIELD

This disclosure relates generally to electronics and more particularlyto reference voltage circuits.

BACKGROUND

A reference voltage circuit is a circuit that produces a fixed voltageto a device. The fixed voltage is substantially constant despitevariations in temperature. In systems on a chip, the current drawn byreference voltage circuit can become a significant contributor to thetotal power drawn by the chip in a power saving mode. Even though thecore logic may not be operating in a power saving mode, the referencevoltage circuit continues to draw current, and may be needed by certaincomponents that continue operating in a power saving mode.

SUMMARY

In some implementations, a microcontroller system includes a higherpower reference voltage circuit and a lower power reference voltagecircuit configured to draw less power than the higher power referencevoltage circuit when enabled. The system includes a power state logiccontroller configured to enable the lower power reference voltagecircuit to provide a first regulated voltage during a power saving mode,and, on exiting the power saving mode, enable the higher power referencevoltage circuit to provide a second regulated voltage. In someimplementations, a microcontroller system includes a main referencevoltage circuit and a secondary reference voltage circuit having afaster startup time than the main reference voltage circuit. The systemincludes a power state logic controller configured to enable the mainreference voltage circuit and the secondary reference voltage circuit onexiting a power saving mode, select the secondary reference voltagecircuit while the main reference voltage circuit is starting up, andselect the main reference voltage circuit when the main referencevoltage circuit is ready.

Particular implementations can provide one or more of the followingadvantages: 1) the system can use less power in power saving mode byswitching to a lower power reference voltage circuit; 2) the system, byselecting between different reference voltage circuits, can select areference voltage circuit that uses less power and has lower accuracywhen higher accuracy components are not in use; 3) the system startuptime on exiting a power saving mode can be reduced compared to someconventional systems; and 4) some modules can be ready to functionsooner after exiting a power saving mode.

The details of one or more disclosed implementations are set forth inthe accompanying drawings and the description below. Other features,aspects, and advantages will become apparent from the description, thedrawings and the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of an example microcontroller system.

FIG. 2 is a flow diagram of an example process performed by amicrocontroller system for entering and exiting a power saving mode.

FIG. 3 is a block diagram of an example microcontroller system.

FIG. 4 is an example timing diagram illustrating the operation of thesystem of FIG. 3.

FIG. 5 is a flow diagram of an example process performed by amicrocontroller system for entering and exiting a power saving mode.

DETAILED DESCRIPTION Example Microcontroller System

FIG. 1 is a block diagram of an example microcontroller system 100. Thesystem includes a power state logic controller 102, a higher powerreference voltage circuit 104, and a lower power reference voltagecircuit 106. The reference voltage circuits are coupled to a number ofmodules by a selection circuit 108. The power state logic controllerconfigures the selection circuit to couple either the higher powerreference voltage circuit or the lower power reference voltage circuitor both to the modules. The modules include a flash memory module 110, avoltage regulator 112, a brown out detector 114, and an analog todigital converter (ADC) 116.

The power state logic controller is configured to enable the lower powerreference voltage circuit to provide a first regulated voltage to theone or more of the modules during a power saving mode, and, on exitingthe power saving mode, enable the higher power reference voltage circuitto provide a second regulated voltage to all of the modules. The powerstate logic controller can toggle the selection circuit to select thehigher power reference voltage circuit instead of the lower powerreference voltage circuit after exiting the power saving mode. Thehigher power reference voltage circuit draws little to no power whendisabled.

In some implementations, the power state logic controller is configuredto disable to the lower power voltage regulator circuit after exitingthe power saving mode. In some other implementations, the power statelogic controller leaves the lower power voltage regulator circuitenabled because its power consumption is not critical in normaloperating mode.

In some implementations, the higher and lower power reference voltagecircuits are configured so that the second reference voltage has ahigher accuracy with respect to a target reference voltage than thefirst reference voltage. For example, the higher power reference voltagecircuit can comprise bipolar transistors that are less prone to varioustypes of drifts but in turn require larger currents, and the lower powerreference voltage circuit can comprise metal-oxide-semiconductor (MOS)transistors which can be used to reduce current consumption.

Some of the modules can be subject to a higher accuracy voltagereference requirement than other modules. For example, some flash memorymodules can run faster with a higher accuracy reference voltage. Some ofthe modules can be disabled during the power saving mode and thenenabled on exiting the power saving mode. For example, the flash memorymodule and the ADC can be disabled during the power saving mode, leavingthe voltage regulator and the brown out detector enabled and dependingon the lower power reference voltage circuit. Then the flash memorymodule and the ADC can be enabled on exiting the power saving mode. Thesystem can include different types of modules, e.g., analog comparators,phase locked loop oscillators, and other modules.

The system can optionally include additional reference voltage circuitshaving varying degrees of power consumption and accuracy. The powerstate logic controller can select a reference voltage circuit having thelowest power consumption that meets the accuracy requirements of theenabled modules.

Example Flow Diagram

FIG. 2 is a flow diagram of an example process 200 performed by amicrocontroller system for entering and exiting a power saving mode. Thesystem can be the example system 100 of FIG. 1.

The system determines to enter the power saving mode (202). For example,the system can receive a request from a user device to enter the powersaving mode, or determine that a threshold period of inactivity haspassed.

The system enables a lower power reference voltage circuit and toggles aselection circuit to select the lower power reference voltage circuit(204). The lower power reference voltage circuit provides a loweraccuracy reference voltage to one or more modules of the system.

The system determines to exit the power saving mode (206). For example,the system can receive a request from a user device to exit the powersaving mode or to perform an operation that the system cannot perform inthe power saving mode.

The system enables a higher power reference voltage circuit and togglesthe selection circuit to select the higher power reference voltagecircuit (208). The higher power reference voltage circuit provides ahigher accuracy reference voltage to one or more additional modules ofthe system, which can be optionally enabled on exiting the power savingmode. The additional modules can be subject to a higher accuracy voltagereference requirement. For example, the additional modules can include aflash memory module, an ADC, or both.

The higher accuracy reference voltage has a higher accuracy with respectto a target reference voltage than the lower accuracy reference voltage.The higher power reference voltage circuit draws more power when enabledthan the lower power reference voltage circuit.

Example Microcontroller System

FIG. 3 is a block diagram of an example microcontroller system 300. Thesystem includes a main reference voltage circuit 302 coupled to a flashmemory module 304 and a voltage regulator 306.

The flash memory module includes a flash core, a secondary referencevoltage circuit 310, and a selection circuit 312. The selection circuitselects between the main reference voltage circuit and the secondaryreference voltage circuit internal to the flash memory module. Thesecondary reference voltage circuit has a faster startup time than themain reference voltage circuit, but the main reference voltage circuithas a higher accuracy with respect to a target reference voltage thanthe secondary reference voltage circuit. For example, the secondaryreference voltage circuit can lack a regulation loop that requires astartup time.

The system includes a power state logic controller 314. The power statelogic controller is configured to enable the main reference voltagecircuit and the secondary reference voltage circuit on exiting a powersaving mode. The power state logic controller configures the selectioncircuit to select the secondary reference voltage while the mainreference voltage is starting up. The power state logic controllerconfigures the selection circuit to select the main reference voltagewhen the main reference voltage circuit is ready.

In some implementations, the power state logic controller is configuredto wait for the secondary reference voltage circuit to be ready afterenabling the secondary reference voltage circuit and, after thesecondary reference voltage circuit is ready, enable the flash memorymodule. The flash memory module can then perform memory accesses duringa time period between enabling the main reference voltage circuit andconfiguring the selection circuit to select the main reference voltagecircuit.

The voltage regulator includes a main regulator 316 and a secondaryregulator 318. The secondary regulator has a lower static currentconsumption than the main regulator, but also produces a regulatedvoltage that has a lower accuracy with respect to a target voltage thanthe main regulator. The lower power regulator includes a secondaryreference voltage circuit 320. The secondary reference voltage circuitcan have a lower static current consumption than the main referencevoltage circuit. The power state logic controller can control theswitching between the main regulator and the secondary regulator.

Example Timing Diagram

FIG. 4 is an example timing diagram 400 illustrating the operation ofthe system 300 of FIG. 3. A timeline 414 illustrates various points intime during the operation of the system.

The “Main ON” signal 402 enables the main reference voltage circuit. The“Main ready” signal 404 indicates that the main reference voltagecircuit is ready. The “Secondary ON” signal 406 enables the secondaryreference voltage circuit. The “Secondary ready” signal 408 indicatesthat the secondary reference voltage circuit is ready. The “Moduleaccess” signal 410 indicates when the module performs some operation,e.g., a memory access to a flash module. The “Wakeup event” line 412indicates when the microcontroller system exits the power saving mode.

At time t1, a wakeup event occurs and the system enables both the mainreference voltage circuit and the secondary reference voltage circuit.At time t2, the secondary reference voltage circuit is ready. At timet3, the module performs an operation, e.g., a flash memory access. Attime t4, the main reference voltage circuit is ready. The system selectsthe main reference voltage circuit instead of or in addition to thesecondary reference voltage circuit, and can optionally disable thesecondary reference voltage circuit.

Because the system uses the secondary reference voltage circuit with afaster startup time than the main reference voltage circuit, the moduleis able to perform operations between t3 and t4. Hence themicrocontroller is able to be useful sooner after exiting the powersaving mode than it would be if it lacked the secondary referencevoltage circuit.

Example Flow Diagram

FIG. 5 is a flow diagram of an example process 500 performed by amicrocontroller system for entering and exiting a power saving mode. Thesystem can be the example system 300 of FIG. 3.

The system determines to enter a power saving mode (502). For example,the system can receive a request from a user device to enter the powersaving mode.

The system disables a main reference voltage circuit (504). The mainreference voltage circuit draws little to no power when disabled.

The system determines to exit the power saving mode (506). For example,the system can receive a request from a user device to exit the powersaving mode or to perform an operation that the system cannot perform inthe power saving mode.

The system enables the main reference voltage circuit and a secondaryreference voltage circuit (508). The secondary reference voltage circuithas a faster startup time than the main reference voltage circuit;hence, the secondary reference voltage circuit will be ready sooner thanthe main reference voltage circuit even though both circuits are enabledat essentially the same time. The main reference voltage circuit and thesecondary reference voltage circuit can be configured so that a mainreference voltage has a higher accuracy with respect to a targetreference voltage than the secondary reference voltage.

The system selects the secondary reference voltage circuit so that thesecondary reference voltage circuit is providing a secondary referencevoltage to a module of the microcontroller system while the mainreference voltage circuit is starting up (510). The module can be aflash memory module or other type of module.

The system optionally performs operations with the module, e.g., memoryaccesses to a flash memory module, when the secondary reference voltagecircuit is ready (512). The system can wait for the secondary referencevoltage circuit to be ready and then, when the secondary referencevoltage circuit is ready, enable the module, which may have beendisabled on entering the power saving mode to save power. Theperformance of the module can be degraded. For example, in the casewhere the module is a flash memory module, the accesses can be done at alower speed.

The system selects the main reference voltage circuit when the mainreference voltage circuit is ready (514) so that the main referencevoltage circuit is providing the main reference voltage to the module.

While this document contains many specific implementation details, theseshould not be construed as limitations on the scope what may be claimed,but rather as descriptions of features that may be specific toparticular embodiments. Certain features that are described in thisspecification in the context of separate embodiments can also beimplemented in combination in a single embodiment. Conversely, variousfeatures that are described in the context of a single embodiment canalso be implemented in multiple embodiments separately or in anysuitable sub combination. Moreover, although features may be describedabove as acting in certain combinations and even initially claimed assuch, one or more features from a claimed combination can, in somecases, be excised from the combination, and the claimed combination maybe directed to a sub combination or variation of a sub combination.

What is claimed is:
 1. A method performed by a microcontroller system,the method comprising: entering a power saving mode; in response toentering the power saving mode, enabling a lower power reference voltagecircuit; after enabling the lower power reference voltage circuit,waiting for the lower power reference voltage circuit to provide a lowerpower reference voltage with a first level of accuracy with respect to atarget reference voltage; when the lower power reference voltage circuitprovides the lower power reference voltage, providing, by the lowerpower reference voltage circuit, the lower power reference voltage toone or more first modules of the microcontroller system; exiting thepower saving mode; in response to exiting the power saving mode,enabling a higher power reference voltage circuit external to the lowerpower reference voltage circuit; after enabling the higher powerreference voltage circuit, waiting for the higher power referencevoltage circuit to provide a higher power reference voltage with asecond level of accuracy with respect to the target reference voltage,wherein the second level of accuracy is higher than the first level ofaccuracy, and the higher power reference voltage circuit draws morepower when enabled than the lower power reference voltage circuit;during a period for the waiting for the higher power reference voltagecircuit to provide the higher power reference voltage, providing, by thelower power reference voltage circuit, the lower power reference voltageto the one or more first modules of the microcontroller system; when thehigher power reference voltage circuit provides the higher powerreference voltage, providing, by the higher power reference voltagecircuit, the higher power reference voltage to the one or more firstmodules of the microcontroller system and one or more second modules ofthe microcontroller system; and on exiting the power saving mode,disabling the lower power reference voltage circuit.
 2. The method ofclaim 1, wherein the lower power reference voltage circuit and thehigher power reference voltage circuit are coupled to the one or morefirst modules and the one or more second modules by a selection circuit,and wherein the method further comprises, on exiting the power savingmode, toggling the selection circuit to select the higher powerreference voltage circuit instead of the lower power reference voltagecircuit.
 3. The method of claim 1, wherein the one or more secondmodules are subject to a higher accuracy voltage reference requirementthan the one or more first modules.
 4. The method of claim 3, whereinthe high power reference voltage circuit provides the higher powerreference voltage with the second level of accuracy higher than thefirst level of accuracy with respect to the target reference voltage byvirtue of the higher power reference voltage circuit comprising aplurality of bipolar transistors and the lower power reference voltagecircuit comprising metal-oxide semiconductor (MOS) transistors.
 5. Themethod of claim 1, wherein the one or more first modules include avoltage regulator and a brownout detector, and wherein the one or moresecond modules includes a flash memory module and an analog to digitalconverter (ADC).
 6. The method of claim 1, further comprising: inresponse to entering the power saving mode, disabling the one or moresecond modules; and in response to exiting the power saving mode,enabling the one or more second modules, wherein the one or more firstmodules are enabled during the power saving mode.
 7. The method of claim1, wherein the microcontroller system comprises a plurality of powerreference voltage circuits including the lower power reference voltagecircuit and the higher power reference voltage circuit, the plurality ofpower reference voltage circuits having varying degrees of powerconsumption and accuracy, wherein the method further comprises: for anenabled module of the microcontroller system, selecting a particularpower reference voltage circuit from the plurality of power referencevoltage circuits, the particular power reference voltage circuit havingthe lowest power consumption that meets accuracy requirements of theenabled module and providing a particular level of accuracy with respectto the target reference voltage; and providing, by the particular powerreference voltage circuit, the target reference voltage to the enabledmodule.
 8. The method of claim 1, further comprising: in response toentering the power saving mode, disabling the higher power referencevoltage circuit so that the higher power reference voltage circuit drawsno power when disabled.
 9. The method of claim 1, wherein the higherpower reference voltage circuit is coupled to a higher voltageregulator, and the lower power reference voltage circuit is coupled to alower voltage regulator.
 10. The method of claim 9, wherein the lowervoltage regulator has a lower static current consumption than the highervoltage regulator, and the lower power reference voltage circuit has alower static current consumption than the higher power reference voltagecircuit.
 11. A microcontroller system comprising: a power state logiccontroller; a higher power reference voltage circuit; a lower powerreference voltage circuit being external to the higher power referencevoltage circuit and configured to draw less power than the higher powerreference voltage circuit when enabled; and one or more first modulesand one or more second modules, wherein the power state logic controlleris configured to: on entering a power saving mode, enable the lowerpower reference voltage circuit to provide a lower power referencevoltage with a first level of accuracy with respect to a targetreference voltage; wait for the lower reference voltage circuit toprovide the lower power reference voltage after enabling the lower powerreference voltage circuit; when the lower power reference voltagecircuit provides the lower power reference voltage, provide the lowerpower reference voltage to the one or more first modules during thepower saving mode, on exiting the power saving mode, enable the higherpower reference voltage circuit to provide a higher power referencevoltage with a second level of accuracy with respect to the targetreference voltage, wherein the second level of accuracy is higher thanthe first level of accuracy, and the higher power reference voltagecircuit draws more power when enabled than the lower power referencevoltage circuit; after enabling the higher power reference voltagecircuit, wait for the higher power reference voltage circuit to providethe higher power reference voltage; during the waiting for the higherpower reference voltage circuit to provide the higher power referencevoltage, provide, by the lower power reference voltage circuit, thelower power reference voltage to the one or more first modules; when thehigher power reference voltage circuit provides the higher powerreference voltage, provide, by the higher power reference voltagecircuit, the higher power reference voltage to the one or more firstmodules and the one or more second modules; and disable the lower powerreference voltage circuit after exiting the power saving mode.
 12. Thesystem of claim 11, further comprising a selection circuit coupled tothe power state logic controller, the higher power reference voltagecircuit, the lower power reference voltage circuit, and the one or morefirst modules and the one or more second modules, wherein the powerstate logic controller is configured to toggle the selection circuit toselect the higher power reference voltage circuit instead of the lowerpower reference voltage circuit after exiting the power saving mode. 13.The system of claim 11, wherein the one or more second modules aresubject to a higher accuracy voltage reference requirement than the oneor more first modules.
 14. The system of claim 13, wherein the highpower reference voltage circuit provides the higher power referencevoltage with the second level of accuracy higher than the first level ofaccuracy with respect to the target reference voltage by virtue of thehigher power reference voltage circuit comprising a plurality of bipolartransistors and the lower power reference voltage circuit comprisingmetal-oxide semiconductor (MOS) transistors.
 15. The system of claim 11,wherein the one or more first modules include a voltage regulator and abrownout detector, and wherein the one or more second modules includes aflash memory module and an analog to digital converter (ADC).
 16. Thesystem of claim 11, wherein the power state logic controller isconfigured to: in response to entering the power saving mode, disablethe one or more second modules; and in response to exiting the powersaving mode, enable the one or more second modules, wherein the one ormore first modules are enabled during the power saving mode.
 17. Thesystem of claim 11, further comprising a plurality of power referencevoltage circuits including the lower power reference voltage circuit andthe higher power reference voltage circuit, the plurality of powerreference voltage circuits having varying degrees of power consumptionand accuracy, wherein the power state logic controller is configured to:for an enabled module of the microcontroller system, select a particularpower reference voltage circuit from the plurality of power referencevoltage circuits, the particular power reference voltage circuit havingthe lowest power consumption that meets accuracy requirements of theenabled module and providing a particular level of accuracy with respectto the target reference voltage; and enable the particular powerreference voltage circuit to provide the target reference voltage to theenabled module.
 18. The system of claim 11, wherein the higher powerreference voltage circuit draws no power when disabled after enteringthe power saving mode.
 19. The system of claim 11, further comprising: ahigher voltage regulator coupled to the higher power reference voltagecircuit, and a lower voltage regulator coupled to the lower powerreference voltage circuit.
 20. The system of claim 19, wherein the lowervoltage regulator has a lower static current consumption than the highervoltage regulator, and the lower power reference voltage circuit has alower static current consumption than the higher power reference voltagecircuit.